Three-phase centrifuge

ABSTRACT

Solids and two liquids, each having different specific gravities, are separated in a centrifuge having a helical screw conveyor mounted within an elongated bowl tapered at one end. A group of solids discharge openings is disposed at the tapered end, and two groups of concentrically arranged liquid discharge openings, one for each separated liquid, are disposed at the other end of the bowl. One group of liquid discharge openings has an annular ring dam mounted adjacent thereto to serve as a weir; the second group of liquid discharge openings has an annular channel disposed adjacent thereto for receiving the separated liquid discharged therethrough, and a skimmer passage disposed within the channel for receiving the liquid within the channel. Optionally, the centrifuge contains a plurality of radially extending ribs mounted adjacent to the two groups of liquid discharge openings for controlling the rotational speed of the separated liquids with respect to the bowl immediately prior to discharge of the liquids. Also, a scraper member is mounted on the screw conveyor for the removal of solids which have accumulated on the inner annular surface of the bowl, and a vane is rigidly mounted between adjacent flights of the conveyor to exclude the lighter of the two separated liquids from the space adjacent to the solids discharge openings.

[72] Inventor AndreL' Lavanchy Devon. Pa. [21] Appl No 7,285 [22] Filed .lan. 30.1970 [45] Patented Nov. 30. 1971 [73] Assignee PennwaltCorporation Philadelphia, Pa.

[54] THREE-PHASE (ENTRIFUGE 13 Claims 5 Drawing Figs.

[52] U.S.Cl. 233/7 233/27, 233/39, 233/41v 233/47 [51] lnt.Cl. .t 1304b 1/00, 1304b 7/00. B04b 1 1/00 [50] FieldofSearch. 233/719. 20.2l.3 27 4.39.4l.46.47

[56] References Cited UNITED STATES PATENTS 1,710,316 4/1929 Laughlin 233/7 2,528,974 11/1950 Ritsch.......... 233/7 3,098,820 7/1963 Gooch 233/7 3,268.159 8/1966 Kern 233/7 3,279,687 10/1966 Amero 233/7 3,285,507 11/1966 Shapiro 1111111 233/7 3,321,131 5/1967 Cook... 233/7 1,572,299 2/1926 McEntire 233/7 2,054,058 9/1936 Laughlin H 233/7 2,873.064 2/1959 Diefenbach... 233/10 FOREIGN PATENTS 998.669 711965 England ABSTRACT: Solids and two liquids. each having different specific gravities. are separated in a centrifuge having a helical screw conveyor mounted within an elongated bowl tapered at one end A group of solids discharge openings is disposed at the tapered end. and two groups of concentrically arranged liquid discharge openings. one for each separated liquid. are disposed at the other end of the bowl One group of liquid discharge openings has an annular ring dam mounted adjacent thereto to serve as a weir; the second group ofliquid discharge openings has an annular channel disposed adjacent thereto for receiving the separated liquid discharged therethrough, and a skimmer passage disposed within the channel for receiving the liquid within the channel Optionally. the centrifuge contains a plurality of radially extending ribs mounted adjacent to the two groups of liquid discharge openings for controlling the rotational speed of the separated liquids with respect to the bowl immediately prior to discharge of the liquids. Also, a scraper member is mounted on the screw conveyor for the removal of solids which have accumulated on the inner annular surface of the bowl, and a vane is rigidly mounted between adjacent flights of the conveyor to exclude the lighter of the two separated liquids from the space adjacent to the solids discharge openings.

g HEAVY PHASE PAENIEBNU 0 m 3.623.656

SHEET 2 BF 2 MAX. DISPL. OF SKIMMER IN VENTOR.

Fig 5 Andre C. Lovcmchy BY Z 7, KW

ATTORNEY.

THREE-PHASE CENTRIFUGE This invention relates to centrifugal separators, but more particularly to a three-phase solid bowl centrifugal separator for separating liquids from finely divided solids, i.e., a centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture.

Conventionally, such a centrifuge comprises an elongated bowl, tapered at one end, and mounted for rotation about an axis. Coaxially mounted within the bowl is a helical screw conveyor which is adapted to rotate at a speed slightly different than the speed of the bowl.

Feed is introduced into the bowl, and due to centrifugal force effected by the rotation of the bowl, the feedseparates into its component parts. Due to the slight difference in the rotational speed between the bowl and the helical screw conveyor, the solids sedimented against the wall are conveyed along the inner annular surface of the bowl to solids discharge openings located at the tapered end of the bowl, while two separated liquids simultaneously exit through separate liquid discharge openings.

Various means exist for discharging separated liquids from the centrifuge bowl. Some centrifuges utilize two liquid discharge conduits, one for each separated liquid. These liquid discharge conduits are supported deep within the central portion of the centrifuge bowl, and although normally stationary, are mounted so as to be radially adjustable. This allows the radial position of the conduits to be changed during rotation of the centrifuge bowl to skim ofi' desired amounts of each of the separated liquids. One difficulty presented with this arrangement is the problem of supporting such conduits deep within a centrifuge bowl which is rotating at an extremely high speed. Another is the necessarily complex arrangements needed to seal against leakage, and to vary the radial positions of the conduits during operation of the centrifuge bowl.

Other centrifuges of the prior art have groups of liquid discharge openings, one group for each separated liquid, disposed in the centrifuge bowl. The openings are arranged and the centrifuge is operated such that during discharge of the separated liquids, each opening is normally completely filled with the liquid being discharged. An individual plate is adjustably mounted adjacent to each opening to vary the size of the opening to control the discharge of the separated liquid. This has the disadvantage of not only being time consuming, but necessitates stopping the centrifuge to make necessary adjustments. Also, varying the size of each opening in this manner has the effect of choking the system which lowers the overall efficiency of the centrifuge. For example, fluid flow through an ordinary conduit is choked when the area of the conduit through which the fluid is flowing is reduced. Greater pressure is required to achieve the same rate of flow through the reduced area. This required increment in pressure is translated in the centrifuge by an inward shift of the liquid level, thereby creating an unbalanced condition. As a result, the line of separation between the separated liquids in the centrifuge bowl also shifts, thereby varying the recovery of the separated materials from that desired. Consequently a three-phase centrifuge is needed which is of relatively simple construction, can be adjusted during the operation thereof, and maximizes the efficiency of the separation process.

Accordingly, one of the principal objects of the present invention is to provide a three-phase centrifuge of relatively simple construction which optimizes the efficiency of the separation process.

Another object of the present invention is to provide a three-phase centrifuge which minimizes the loss of one of the separated liquids through the solids discharge openings.

Another object of the present invention is to provide a centrifuge which prevents the accumulation of solids along the inner annular wall of the centrifuge bowl.

Another object of the present invention is to provide a three-phase centrifuge which prevents relative rotation between the separated liquids and the centrifuge bowl immediately prior to discharge ofthe liquids.

Another object of the present invention is to provide a three-phase centrifuge in which the line of separation between two separated liquids is adjustable during the operation of the centrifuge.

Another object of the present invention is to provide a three-phase centrifuge having a wider range of potential adjustment of the line of separation between two separated liquids.

Another object of the present invention is to provide a three-phase centrifuge in which major adjustments for the separation process can be made before the centrifuge is put into operation, and minor adjustments can be made during the operation of the centrifuge.

Another object of the present invention is to provide a three-phase centrifuge which prevents discharge of any interfacial emulsion layer along with one of the desired separated liquids.

Briefly, the present invention seeks to accomplish such objects by providing a countercurrent three-phase centrifuge having an annular ring dam disposed adjacent to a first group of liquid discharge openings for initial and major adjustment of the E-line, i.e., the line of separation between two liquid phases within a centrifuge bowl. Further provided is a skimming means mounted adjacent to a second group ofliquid discharge openings for fine adjustment of the E-line during the operation of the centrifuge, each group of liquid discharge openings being disposed in the same end of the centrifuge bowl. The centrifuge is also provided with means for preventing loss of one of the separated liquids through the solids discharge openings, and with means for preventing the accumulation of solids on the inner annular surface of the bowl. Also provided is a series or plurality of radially extending ribs mounted adjacent to the first and second groups of liquid discharge openings for preventing relative rotation between the separated liquids and bowl immediately prior to discharge of the liquids.

In the drawings:

FIG. 1 is an elevational view of a three-phase centrifuge embodying the invention with a portion broken away to show the interior thereof in section;

FIG. 2 is an enlarged sectional view, showing the liquid discharge end of the centrifuge in detail;

FIG. 3 is an enlarged view, taken along line 3-3 of FIG. 2 showing the plurality of radially extending ribs mounted adjacent to the liquid discharge outlets;

FIG. 4 is an enlarged view, taken along line 44 of FIG. 1, showing a vane mounted on the hub ofthe helical conveyor;

FIG. 5 is an enlarged view showing a mechanical linkage for controlling a skimmer passage as embodied in the present invention.

Referring to FIG. 1 of the drawings, there is illustrated a three-phase centrifuge, designated generally by the numeral 10, having an imperforate centrifuge bowl l2, journaled at the ends thereof in main bearings 13 and 15. The bowl 12 is disposed within a cover 14, and adapted to be belt driven by a motor (not shown), the belt extending around a pulley 16. The centrifuge bowl 12 is capable of being rotated, about an axis through the center thereof, at speeds which will generate a centrifugal force equal to several thousand times the force of gravity. Disposed within the bowl 12 is a helical screw conveyor 18 adapted to rotate at a speed that is slightly different than that of the bowl 12. The helical conveyor 18 includes coiled screw flights 20, the distal edges of the screw flights 20 generally complementing the inside contour of the bowl 12. The bowl 12 and the conveyor 18 are mounted in coaxial relationship.

It is to be noted that the axially elongated bowl 12 is mainly of imperforate cylindrical construction. However, the end portion 22 of the bowl adjacent to end wall 24 is of convergent or truncoconical form, its inner annular surface gradually decreasing in diameter toward the end wall 24.

Disposed within the end portion 22, and adjacent to end wall 24, is a group of solids discharge openings 26 symmetrically arranged about the rotational axis. Disposed at the other end of bowl 12 is an end member 28. Integral with end member 28 is a front hub 29 which is supported within main bearing 13. A first group of liquid discharge openings 30 is symmetrically disposed with respect to the axis of rotation within end member 28 adjacent to the inner annular face of bowl 12. A second group of liquid discharge openings 32 is symmetrically disposed within end member 28 at a lesser radial distance from the axis of rotation than openings 30. As can be seen in FIG. 2, and which will be more fully explained later, during rotation of the bowl 12 the liquids separate into two concentric pools, heavy liquid phase discharging through openings 30, while light liquid phase is discharging through openings 32.

The helical screw conveyor I8, being hollow, has a feed chamber 34 disposed therein. The process feed stream, or liquids-solids mixture to be separated, is introduced into feed chamber 34 through an axially extending feedpipe 36. This mixture is then delivered from feed chamber 34, through a plurality of radially extending passages 38 disposed within the helical conveyor 18, into a separation chamber 40. As illustrated in FIG. 1, the separation chamber 40 is defined by the inner surface of the bowl 12 and the helical conveyor 18.

Mounted within the bowl l2, and adjacent to liquid discharge openings 32, is an annular ring darn 42. This ring darn 42 acts as a weir, over which light liquid phase flows on being discharged through liquid discharge openings 32. Ring dam 42 is available in various sizes depending on the relative specific gravities of the two liquid phases to be separated. Thus, by knowing the concentration ofa mixture, and the relative specific gravities of each phase of the mixture, a. proper size ring dam can be selected which will provide a self-regulating centrifugal separation system. Using the selected ring dam, and assuming the concentration and the relative specific gravities of the phases remain constant, the position of the E-line, i.e., the line of separation between the two liquid phases, is fixed within the centrifuge bowl during the rotation thereof. Thus, by fixing the exact location of the E-line, the purity of the recovered phases can be controlled, i.e., there will be no intermingling of the two liquid phases being discharged. It is to be noted that openings 32 are disposed and the centrifuge operated in a manner such that light liquid phase discharging through the openings 32 does not completely fill the openings, and the ring dam 42 acts only as a weir and does not reduce the flow area of the discharge passage actually used for conducting liquid since the latter is generously oversized. This is to be distinguished from arrangements having flow passages which are choked to control the rate at which liquid discharges from the centrifuge bowl. Arrangements which choke the discharge parts have the undesirable effect of shifting the position of the E-line within the centrifuge bowl, thus preventing recovery of the desired separated materials and reducing the overall efficiency of the separation process.

Mounted within bowl l2, and adjacent to ring dam 42, is an underdam ring 44, which partially extends over liquid discharge openings 30, as shown in FIG. 3. This underdam ring 44 is provided to compensate for a possible emulsion layer between the two liquid phases and to increase the range of potential E-line adjustment. By partially extending over openings 30, underdam ring 44 prevents the discharge therethrough of any emulsion which might form as a layer between the two liquid phases. The ring 44 also blocks light liquid phase from discharging through the liquid discharge openings 30.

As best shown in FIG. 3, a plurality of radially extending ribs 46 is mounted to the face of underdam ring 44. These ribs 46 are symmetrically disposed around the circumference of the face of underdam ring 44, and extend over openings 30 and 32. In order to reduce the turbulence of the liquids being discharged through openings 30 and 32, an annular screen member 48 is removably mounted to the faces of the ribs 46, the screen member extending in a radial direction to the same extent as the ribs 46. The screen member 48, with its flowdirecting apertures, is an optional accessory which can be removed when not needed.

The ribs 46 serve to maintain zero relative rotational velocity between the liquids and bowl I2 by acting as abutting means for liquid particles tending to increase or decrease in rotational velocity with respect to the bowl. For example, if a liquid particle rotating at the same velocity as the bowl moves inwardly toward the axis of rotation, it will tend to increase in velocity. However, any liquid particle doing the same as it moves between adjacent ribs will immediately contact the edge of one of the ribs 46 which will thus halt movement of the liquid particle with respect to the bowl 12. Maintaining zero relative rotational velocity between the separated liquids and the bowl I2 is necessary to prevent shifting the position of the E-line during the separation process. An undesired change in the position of the E-line prevents achievement of the desired separation results.

As shown in FIGS. I and 4, a vane member 68 is mounted on helical screw conveyor 18. The latter extends between adjacent flights of the conveyor 18 at the right hand or solids discharge end of separation chamber 40. This vane 68 is axially located on screw conveyor 18 immediately adjacent to the plurality of radially extending passages 38 (See FIG. 1). As can be seen, the upper edge of vane 68 extends above the E- line or line of separation between the two liquid phases, and acts as a rotating dam which allows only heavy liquid phase to flow to this converging portion of separation chamber 40.

Also mounted on helical screw conveyor 18 is a scraper member 70. Scraper member 70 is positioned on the periphery of the flight adjacent to end member 28. Upon rotation of the helical screw conveyor 18, scraper member 70 removes any accumulations ofsolids on the inner annular surface of the centrifuge bowl adjacent to liquid discharge openings 30. This prevents clogging of the openings 30, and allows these accumulations of solids to be loosened, and conveyed toward the solids discharge openings 26 by the helical screw conveyor 18.

Referring to FIG. 2, it can be seen that an annular generally cup-shaped member 50 is mounted to the exterior side of end member 28. This cup-shaped member 50 is comprised of a base portion 51 and an annular flange portion 53. It is noted that the inner annular surface of the flange portion 53 increases in diameter in a direction extending away from the base portion 51. An annular zone 55 is thus defined by the outer surface of the bowl l2 and the inner annular surface of the flange portion 55. Integral with the base portion 51 is a radially extending rim 52. Thus, as can be seen, an annular channel 54 is defined by the annular cup-shaped 50 and end member 28, the channel 54 being disposed adjacent to liquid discharge openings 30. Thus, heavy liquid phase is discharged into the annular channel 54 during rotation of the centrifuge bowl 12.

As shown in FIG. 2, disposed within the annular channel 54 is a skimmer tube 56. This skimmer tube 56 has a liquid inlet 58 See FIG. 5 disposed therein for receiving the heavy liquid phase from the annular channel 54, and a liquid outlet 59 for discharging the heavy liquid phase.

The skimmer tube 56 is mounted so that it can be radially moved into or out of channel 54 to receive more or less of the heavy liquid phase within the channel. A suitable mechanism for radially moving the skimmer tube into or out ofchannel 54 is illustrated in FIG. 5. The skimmer tube 56 is actuated through a crank 82, a threaded bolt 84, a slide member 89, a lever rod 85, and an eccentrically mounted skimmer ring 80, the threaded bolt 84 being threadably connected to the slide member 89. As can be seen, upon rotating the crank 82 the slide member 89 will slide into or out of the cover 14 and thus vary the radial position of the skimmer tube 56. The adjustment range of the bolt 84 is limited by practical space considerations. Increased travel of skimmer tube 56 is obtained by changing the position of the connection between the slide member 89 and lever rod 85. As can be seen in FIG. 5, slide member 89 and lever rod 85 are held together by a removable pin at one of three positions, i.e., 86, 87, or 88. It is to be noted that the skimmer tube 56 is welded to the skimmer ring 80 so that liquid passes through the skimmer tube 56, outlet 59, and into a generally tangentially extending channel 81 formed in the skimmer ring 80. The present arrangement for radially moving the skimmer tube 56 is only one means for doing so. Other means, many of which are well known in the art, are equally satisfactory for moving the tube.

As best shown in FIG. 2, disposed on the outer periphery of the annular cup-shaped member 50 are two annular grooves 60 and 61. As can be seen, these grooves cooperate with two annular partitions 62 and 63 respectively to define two annular spaces 65 and 67 between the centrifugal bowl l2 and the cover 14. Because the member 50 rotates with centrifuge bowl 12, and the partitions 62 and 63 are stationary, this construction effectively seals the annular space 65 from the annular space 67 during operation of the centrifuge. It can be seen that light liquid phase will be discharged into annular space 65 via openings 32 and annular zone 55, while heavy liquid phase is discharged into annular space 67 via openings 30, annular channel 54, skimmer tube 56, and channel 81. The separated liquids are recovered from annular spaces 65 and 67 through appropriate discharge outlets (not shown).

Referring to FIGS. 2 and 3, the particular arrangement of liquid discharge openings and 32 will be described in greater detail. It is first noted that openings 30 and 32 are not angularly aligned, but that openings 32 are located between adjacent openings 30. This allows for the crossover arrangement, i.e., openings 30 extend from the interior to the exterior of bowl 12 in a radially inward direction, while openings 32 extend from the interior to the exterior of the bowl in a radially outward direction. It can also be seen that each of the openings 30 forms a single extended passageway extending from separation chamber to annular channel 54, while each of the openings 32 includes a distinct passageway 33 extending the openings 32 to the outer annular surface of end member 28. Thus, heavy liquid phase and light liquid phase are discharged in opposite directions, i.e., heavy liquid phase is discharged radially inward from separation chamber 40, via openings 30, and into annular channel 54, while light liquid phase is discharged radially outward from separation chamber 40, via openings 32, passageways 33, and into annular zone 55.

In operation, the process feed stream, or liquids-solids mixture to be separated, is delivered through feed tube 36 into feed chamber 34, through radial passages 38, and into the separation chamber 40. Under the influence of centrifugal force, the mixture forms a layer against the inner annular surface of bowl 12, the solid particles being urged by reason of their high specific gravity to form a layer immediately next to the inner annular surface of the bowl, while the lighter liquid tends to rise toward the center of the bowl. The liquid will separate into two concentric pools toward the center of the bowl, the heavy liquid phase being that pool nearest the inner annular surface ofthe bowl.

As aforesaid, because the bowl 12 and the helical screw conveyor 18 are operating at slightly different speeds, solids are moved axially to the right, along the inner annular surface of bowl 12, up the inner annular surface of the end portion 22, and are discharged through solids discharge openings 26. Ordinarily, as the solids are moving along the inner annular surface of the end portion 22, they would pass through both liquid phases. Thus, a portion of each of the liquid phases would be washed out through the solids discharge openings 26 with the solids. However, vane 68 on the helical conveyor 18 acts as a rotating dam. As previously stated, the upper edge of vane 68 extends above the E-line, or the line of separation between the two liquid phases. Thus, the lighter of the two phases or that pool nearest the axis of rotation is efiectively dammed 05 from this portion of the separation chamber. Therefore, vane 68 serves to allow recovery of more of the light liquid phase because it is not carried out the solids discharge openings 26 with the discharged solids.

Simultaneously, the two liquid phases are being discharged through openings 30 and 32. Light liquid phase is discharged through openings 32, while heavy liquid phase is discharged through openings 30. As previously stated, ring dam 42 is available in various sizes depending on the relative specific gravities of the two liquid phases. Thus, by knowing the concentration of the mixture, and the relative specific gravities of the phases to be separated, a proper size ring dam can be selected before operation of the centrifuge is begun which predetermines the position of the E-line or line of separation between the two liquid phases. Therefore, the major adjustment of the E-line is made before the separation process is begun by selecting the proper size ring dam 42. As previously stated, the underdam ring 44 is provided to increase the range of potential E-line adjustment, and compensate for a possible emulsion layer. As can be seen in FIG. 2, underdam ring 44 extends partially over liquid discharge openings 30. Therefore, only the desired heavy liquid phase is discharged through openings 30, the underdam ring preventing the discharge of any interfacial emulsion, or light liquid phase.

Thus, heavy liquid phase is discharged through openings 30, into annular channel 54, into skimmer tube 56 and into the annular space 67. As previously stated, the skimmer tube 56 is radially movable so that its liquid inlet 58 can be moved into or out of the channel 54 to recover more or less heavy liquid phase therefrom. When the liquid inlet 58 is moved into the annular channel 54 to contact the liquid therein, the dynamic pressure of the rotating liquid coming into contact with the inlet 58 promotes the flow ofliquid through the skimmer tube 56, and thus reduces the depth of the heavy liquid phase pool, and consequently the E-line position is changed. This serves to optimize performance either under static conditions, or in response to slight variations in the relative specific gravities of the two liquid phases, or to variations in the relative concentration of the two liquid phases. Thus, skimmer tube 56 provides for the fine adjustment of the E-line position without stopping the centrifuge. Also, location of skimmer tube 56 on the exterior of bowl 12 allows for a more simplified construction, and eliminates the problem of supporting and sealing a skimmer tube extending deep into the central portion of the centrifuge bowl.

Thus, the present invention optimizes the efiiciency of the separation process by providing means to prevent, or compensate for, various conditions which may occur during the operation of the centrifuge, which conditions would normally prevent obtaining the desired separation results.

What is claimed is:

l. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising:

a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings;

b. annular ring darn means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged;

c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl;

d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl,

discharge openings;

b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged;

serving as a weir over which said second liquid flows upon being discharged;

. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an said outlet being adapted to introduce said feed into said axially elongated hub radially spaced from said how] to separating chamber; define therewith an annular separating chamber, flights e. and vane means mounted on said hub and extending mounted on said hub for movement therewith, said flights between adjacent flights, said vane means being located having their distal edges generally complementing the inadjacent said portion of said inner annular surface which side contour of said bowl;

is decreasing in diameter, said vane means being adapted 10 (1. feed means having an outlet, said outlet being positioned to exclude said second liquid from that portion of the between said one end and said other end of said bowl, separation chamber in which said vane means is posisaid outlet being adapted to introduce said feed into said tioned. separating chamber;

2. A three-phase centrifuge for separating solids, a first e. and means defining an annular channel on the exterior of liquid, and a second liquid, each having different specific said other end adjacent to said first group of liquid gravities, from feed comprising a liquids solids mixture, said discharge openings, said annular channel opening in an centrifuge comprising; inward direction and being adapted to receive said first a. an elongated hollow bowl of circular cross section liquid discharged through said first group of liquid mounted for rotation about an axis, said bowl having an discharge openings, and further including a skimmer tube inner annular surface with aportion thereof decreasing in having an inlet for receiving said first liquid from said diameter approaching one end of said bowl, said bowl channel, said inlet being disposed within said channel, having a solids discharge opening disposed at said one said first group of liquid discharge openings extending end, the other end of said bowl having disposed therein a from the interior to the exterior of said bowl in a radially first group of liquid discharge openings for discharge of inward direction, and said second group of liquid the first liquid, and a second group of liquid discharge discharge openings extending from the interior to the exopenings for discharge of the second liquid, said second terior of said bowl in a radially outward direction, said group of liquid discharge openings opening into the infirst group of liquid discharge openings terminating adterior of said bowl at said other end at a lesser distance jacent said annular channel, said second group of liquid from the axis of rotation than said first group of liquid discharge openings terminating at the outer annular surface of said bowl.

4. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising:

0. a screw conveyor disposed within said bowl and mounted a. an elongated hollow bowl of circular cross section for coaxial rotation therein, said conveyor including an mounted for rotation about an axis, said bowl having an axially elongated hub radially spaced from said bowl to inner annular surface with a portion thereof decreasing in define therewith an annular separating chamber, flights diameter approaching one end of said bowl, said bowl mounted on said hub for movement therewith, said flights having a solids discharge opening disposed at said one having their distal edges generally complementing the inend, the other end of said bowl having disposed therein a side contour of said bowl; first group of liquid discharge openings for discharge of d. feed means having an outlet, said outlet being positioned the first liquid, and a second group of liquid discharge between said one end and said other end of said bowl, openings for discharge of the second liquid, said second said outlet being adapted to introduce said feed into said group of liquid discharge openings opening into the inseparating chamber; terior of said bowl at said other end at a lesser distance e. radically extending rib means mounted adjacent to said from the axis of rotation than said first group of liquid other end, said radially extending rib means being discharge openings, said first group of openings extending adapted to control the rotational velocity of one of said from the interior to the exterior of said bowl in a radially liquids with respect to said bowl; inward direction, said second group of openings extendf. and screen means mounted adjacent said plurality of radiing from the interior to the exterior of said bowl in a radially extending ribs, said screen means being adapted to reduce the turbulence of said first liquid and said second liquid being discharged through said first and said second groups of liquid discharge openings.

3. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising:

a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said how] having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings;

b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring darn means ally outward direction, said second group of liquid discharge openings terminating at the outer annular surface of said bowl;

b. annular ring dam means mounted adjacent to said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged;

c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl;

d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber.

5. A three-phase centrifuge according to claim 4 including an annular cup-shaped member, said cup-shaped member comprising a base portion and an annular flange portion extending from said base portion, said flange portion having an inner annular surface which increases in diameter in a direction away from said base portion, said base portion mounted to the exterior of said other end and said flange portion extending in a direction toward said one end of said bowl, the inner annular surface of said flange portion and the outer annular surface of said bowl defining an annular zone, the outer annular surface of said flange portion having a plurality of annular grooves disposed therein. means surrounding said flange portion and cooperating with said annular grooves to define a first space and a second space on either side of said means, said annular cup-shaped member and said means being adapted to rotate with respect to each other, said annular zone communicating with said second space, said first group of liquid discharge openings extending from the interior of said bowl to said first space, and said second group of liquid discharge openings extending from the interior of said bowl to said annular zone.

6. A three-phase centrifuge according to claim in which said base portion includes a radially inwardly extending rim defining an annular channel between said base portion and said other end, said annular channel being disposed adjacent said first group ofliquid discharge openings.

7. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising:

a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings;

b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring darn means serving as a weir over which said second liquid flows upon being discharged;

c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl;

d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber;

e, and means defining an annular channel on the exterior of said other end adjacent to said first group of liquid discharge openings, said annular channel opening in an inward direction and being adapted to receive said first liquid discharged through said first group of liquid discharge openings, and further including a skimmer tube having an inlet for receiving said first liquid from said channel, said inlet being disposed within said channel.

8. A three-phase centrifuge according to claim 7, including annular underdam ring means mounted adjacent said group of liquid discharge openings, said annular underdam ring means being adapted to prevent discharge of said second liquid through said first group ofliquid discharge openings 9. A three-phase centrifuge according to claim 7 including a radially extending rib means mounted on the interior of said bowl adjacent said other end, said radially extending rib means being adapted to control the rotational velocity of one of said liquids with respect to said bowl and annular underdam ring means mounted adjacent said first group of liquid discharge openings, said annular underdam ring means being adapted to prevent discharge of said second liquid through said first group of liquid discharge openings.

10. A three-phase centrifuge for separating solids, a first liquid and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising:

a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings;

b means defining an annular channel on the exterior of said other end adjacent said first group of liquid discharge openings, said annular channel being adapted to receive said first liquid discharged through said first group of liquid discharge openings and further including a skimmer tube having an inlet for receiving said first liquid from said annular channel, said inlet being disposed within said channel;

c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl;

d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber.

11. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising:

a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings;

b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged;

c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl;

d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber;

e. annular underdam ring means mounted adjacent said first group of liquid discharge openings, said annular underdam ring means being adapted to prevent discharge of said second liquid through said first group of liquid discharge openings.

12. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising:

13. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising:

a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one diameter approaching one end of said bowl, said bowl end, the other s q a bowl as p therein 3 having a solids discharge opening disposed at said one groul? hqud mscharge opemngs fhscbarge of end, the other end of said bowl having disposed therein a the fi liquid; and a Second g oup of ll quid discharge first group of liquid discharge openings for discharge of opemngs f of the T' i the first liquid, and a second group of liquid discharge of 9"" dlscharg? Opemngs Openmg mm l5 tenor of said bowl at said other end at a lesser distance openings for discharge of the second liquid, said second from the axis of rotation than said first group of liquid group of liquid discharge openings opening into the indis hat 0 ni terior of said bowl at said other end at a lesser distance b c I d d from the axis of rotation than said first group of liquid annu at i means a l Sal sewn h group of liquid discharge openings, said ring dam means arge P serving as a weir over which said second liquid flows upon b. annular ring dam means mounted ad acent said second being discharged;

of liquid, discharg? operfings said F dam means c. a screw conveyor disposed within said bowl and mounted seitvmgfm over when Sam second flows upon for coaxial rotation therein, said conveyor including an bemg dlscharged; axially elongated hub radially spaced from said bowl to c a screw conveyor disposed within said bowl and mounted d fi therewith an lar separating chamber, flights for coaxial rotation therein, said conveyor including an mounted on Said hub for movement (herewim Said flights axially elongated hub radially Spaced fmm Said bowl to having their distal edges generally complementing the indefine therewith an annular separating chamber, flights side contour f id bOW]; mounted Said hub for movement therewith, Said flights d. feed means having an outlet, said outlet being positioned having heir is l ge genera y comp e en g the between said one end and said other end of said bowl, Side COHIOUI OfSaid bowl; said outlet being adapted to introduce said feed into said d. feed means having an outlet, said outlet being positioned separating chamber;

between said one end and said other end of said bowl, e. a scraper member mounted adjacent the distal edges of said outlet being adapted to introduce said feed into said one of said flights, said scraper member being disposed separating chamber; adgacent said inner annular surface, and adjacent said e. radially extending rib means mounted adjacent to said h er end of i bowl! f adapted to rotate about Sald end, Said radially exmnding rib means being axis upon rotation of said screw conveyor to remove acadapted to control the rotational velocity of one of said cumulanons of Sohds on Sald mner annular surface liquids with respect to said bowl.

2% 'UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 555 Dated November 30. 1971 Inventor(s) ndre C. Lavanchy It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 4, line 46 after the words "cup-shaped" insert member In column 5, line 13 the word "centrifugal" should read centrifuge-- In column 9, line65 insert the word "first" after said and before "group" Signed and sealed this 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising: a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings; b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged; c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl; d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber; e. and vane means mounted on said hub and extending between adjacent flights, said vane means being located adjacent said portion of said inner annular surface which is decreasing in diameter, said vane means being adapted to exclude said second lIquid from that portion of the separation chamber in which said vane means is positioned.
 2. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising; a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings; b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged; c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl; d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber; e. radically extending rib means mounted adjacent to said other end, said radially extending rib means being adapted to control the rotational velocity of one of said liquids with respect to said bowl; f. and screen means mounted adjacent said plurality of radially extending ribs, said screen means being adapted to reduce the turbulence of said first liquid and said second liquid being discharged through said first and said second groups of liquid discharge openings.
 3. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising: a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings; b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged; c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl; d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber; e. and means defining an annular channel on the exterior of said other end adjacent to said first group of liquid discharge openiNgs, said annular channel opening in an inward direction and being adapted to receive said first liquid discharged through said first group of liquid discharge openings, and further including a skimmer tube having an inlet for receiving said first liquid from said channel, said inlet being disposed within said channel, said first group of liquid discharge openings extending from the interior to the exterior of said bowl in a radially inward direction, and said second group of liquid discharge openings extending from the interior to the exterior of said bowl in a radially outward direction, said first group of liquid discharge openings terminating adjacent said annular channel, said second group of liquid discharge openings terminating at the outer annular surface of said bowl.
 4. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising: a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings, said first group of openings extending from the interior to the exterior of said bowl in a radially inward direction, said second group of openings extending from the interior to the exterior of said bowl in a radially outward direction, said second group of liquid discharge openings terminating at the outer annular surface of said bowl; b. annular ring dam means mounted adjacent to said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged; c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl; d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber.
 5. A three-phase centrifuge according to claim 4 including an annular cup-shaped member, said cup-shaped member comprising a base portion and an annular flange portion extending from said base portion, said flange portion having an inner annular surface which increases in diameter in a direction away from said base portion, said base portion mounted to the exterior of said other end and said flange portion extending in a direction toward said one end of said bowl, the inner annular surface of said flange portion and the outer annular surface of said bowl defining an annular zone, the outer annular surface of said flange portion having a plurality of annular grooves disposed therein, means surrounding said flange portion and cooperating with said annular grooves to define a first space and a second space on either side of said means, said annular cup-shaped member and said means being adapted to rotate with respect to each other, said annular zone communicating with said second space, said first group of liquid discharge openings extending from the interior of said bowl to said first space, and said second group of liquid discharge openings extending from the interior of said bowl to said annular zone.
 6. A three-phase centriFuge according to claim 5 in which said base portion includes a radially inwardly extending rim defining an annular channel between said base portion and said other end, said annular channel being disposed adjacent said first group of liquid discharge openings.
 7. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising: a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings; b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged; c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl; d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber; e. and means defining an annular channel on the exterior of said other end adjacent to said first group of liquid discharge openings, said annular channel opening in an inward direction and being adapted to receive said first liquid discharged through said first group of liquid discharge openings, and further including a skimmer tube having an inlet for receiving said first liquid from said channel, said inlet being disposed within said channel.
 8. A three-phase centrifuge according to claim 7, including annular underdam ring means mounted adjacent said group of liquid discharge openings, said annular underdam ring means being adapted to prevent discharge of said second liquid through said first group of liquid discharge openings.
 9. A three-phase centrifuge according to claim 7 including a radially extending rib means mounted on the interior of said bowl adjacent said other end, said radially extending rib means being adapted to control the rotational velocity of one of said liquids with respect to said bowl and annular underdam ring means mounted adjacent said first group of liquid discharge openings, said annular underdam ring means being adapted to prevent discharge of said second liquid through said first group of liquid discharge openings.
 10. A three-phase centrifuge for separating solids, a first liquid and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising: a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance frOm the axis of rotation than said first group of liquid discharge openings; b. means defining an annular channel on the exterior of said other end adjacent said first group of liquid discharge openings, said annular channel being adapted to receive said first liquid discharged through said first group of liquid discharge openings and further including a skimmer tube having an inlet for receiving said first liquid from said annular channel, said inlet being disposed within said channel; c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl; d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber.
 11. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising: a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings; b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged; c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl; d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber; e. annular underdam ring means mounted adjacent said first group of liquid discharge openings, said annular underdam ring means being adapted to prevent discharge of said second liquid through said first group of liquid discharge openings.
 12. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising: a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings; b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged; c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl; d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber; e. radially extending rib means mounted adjacent to said other end, said radially extending rib means being adapted to control the rotational velocity of one of said liquids with respect to said bowl.
 13. A three-phase centrifuge for separating solids, a first liquid, and a second liquid, each having different specific gravities, from feed comprising a liquids-solids mixture, said centrifuge comprising: a. an elongated hollow bowl of circular cross section mounted for rotation about an axis, said bowl having an inner annular surface with a portion thereof decreasing in diameter approaching one end of said bowl, said bowl having a solids discharge opening disposed at said one end, the other end of said bowl having disposed therein a first group of liquid discharge openings for discharge of the first liquid, and a second group of liquid discharge openings for discharge of the second liquid, said second group of liquid discharge openings opening into the interior of said bowl at said other end at a lesser distance from the axis of rotation than said first group of liquid discharge openings; b. annular ring dam means mounted adjacent said second group of liquid discharge openings, said ring dam means serving as a weir over which said second liquid flows upon being discharged; c. a screw conveyor disposed within said bowl and mounted for coaxial rotation therein, said conveyor including an axially elongated hub radially spaced from said bowl to define therewith an annular separating chamber, flights mounted on said hub for movement therewith, said flights having their distal edges generally complementing the inside contour of said bowl; d. feed means having an outlet, said outlet being positioned between said one end and said other end of said bowl, said outlet being adapted to introduce said feed into said separating chamber; e. a scraper member mounted adjacent the distal edges of one of said flights, said scraper member being disposed adjacent said inner annular surface, and adjacent said other end of said bowl, and adapted to rotate about said axis upon rotation of said screw conveyor to remove accumulations of solids on said inner annular surface. 